Spin transfer based Magnetic Random Access Memory (MRAM) is a second generation MRAM technology that may offer the advantages of the first generation MRAM without the drawbacks of poor scalability and high write current. For example, FIGS. 1-2 depict a portion of a conventional spin transfer torque magnetic random access memory (STT-RAM). FIG. 1 depicts a small portion of the STT-RAM 1 including a storage cell 10. The conventional STT-RAM 1 includes a conventional magnetic storage cell 10 including a magnetic element 12 and a selection device 14. The selection device 14 is generally a transistor such as a NMOS transistor and includes a drain 11, a source 13, and a gate 15. Also depicted are a word line 16, a bit line 18, and source line 20. The word line 16 is oriented perpendicular to the bit line 18. The source line 20 is typically either parallel or perpendicular to the bit line 18, depending on specific architecture used for the conventional STT-RAM 1. The bit line 18 is connected to the magnetic element 12, while the source line 20 is connected to the source 13 of the selection device 14. The word line 16 is connected to the gate 15. FIG. 2 depicts the magnetic element 12. The magnetic element 12 includes an antiferromagnetic (AFM) layer 30, a pinned or reference layer 32, a nonmagnetic spacer layer 34, and a free layer 36. The AFM layer 30 is used to pin the magnetization 33 of the reference layer 32. The reference layer 32 may be a multilayer such as a synthetic antiferromagnet (SAF). The spacer layer 34 may be a conductor, such as Cu or an insulating tunneling barrier layer, such as crystalline MgO. The free layer has a magnetization 37 that may be switched.
The conventional STT-RAM 1 programs the magnetic memory cell 10 by driving a bi-directional current through the cell 10. In particular, the magnetic element 12 is configured to be changeable between a high resistance state (free layer magnetization 37 antiparallel to pinned layer magnetization 33) and a low resistance state (free layer magnetization 37 parallel to pinned layer magnetization 33) by a current flowing through the conventional magnetic element 12. When a current having a sufficiently large current density is passed perpendicular to plane, a torque sufficient to switch the magnetization 37 is generated. Typically, the requisite current density is achieved by ensuring that the magnetic element 12 ha a sufficiently small cross-sectional area as well as other features desirable for switching using the spin transfer effect.
Although the conventional STT-RAM 1 functions, one of ordinary skill in the art will readily recognize that the STT-RAM 1 is still desired to be improved.